Composite electrode and method of making same

ABSTRACT

A composite electrode includes two opposing sheets of titanium spaced apart in a central portion and sealed together around their edges to form an envelope. A mass of work-hardened copper wool or shredded copper is disposed in a compressed state within the envelope to provide a core of substantially greater electrical conductivity than that of the titanium sheets, which protect the copper from chemical corrosion.

[4 1 Sept. 23, 1975 United States Patent 1191 Paige et al.

[5 COMPOSITE ELECTRODE AND METHOD 3,278,410 10/1966 Nelson.............

Ruthel et al.....

OF MAKING SAME 9/1973 Ruthel et al..... 204/290 1= [75] Invent rs: t r M- Paig Placentia; mi 4/1974 204/58 FOREIGN PATENTS OR APPLICATIONS Scherba, Anaheim, both of Calif.

[ Assigneel l Narver, 1119-, Anaheim 7,023,016 6/1966 204/290F Ca l 1 182210 11/1964 Germany......................... 204/290F OTHER PUBLICATIONS Defensive Publication 689,485 by Tor Pub. 3/69, 860 O6 1008.

[22] Filed: Apr. 4, 1974 21 Appl. No.2 457,787

Primary ExaminerF. C. Edmund son Attorney, Agent, or Firm-Christie, Parker & Hale [57] ABSTRACT A composite electrode includes two opposing sheets of titanium spaced apart in a central portion and ZR%0 9 /2 Q9 H 4n 6 0 3 2 0 H4 6 .suo 8 4 2 o M U 0 3n 2 km l F 0 m B" 0 9 u 2 u 4 "m 0 "u 2 a mhr c r "a e S M .m a. .mF N 55 .III.

[56] References Cited UNITED STATES PATENTS sealed together around their edges to form an envelope. A mass of work-hardened copper wool or shredded copper is disposed in a compressed state within the envelope to provide a core of substantially greater electrical conductivity than that of the titanium sheets, which protect the copper from chemical corrosion.

6 Claims, 7 Drawing Figures 7 8237 3%4B4Q 4 0404 0/2020 Z4 .12 2 .0 n mmu m u" n a m t WSB re oP u i I mm M n u e MPHPDW 683895 934556 0099999 HHHHHH 0 02 2 22 20 2 737 94 573 603662 22223 lrliii'li" US Patent Sept. 23,1975 shw 1 of 3 3,907,659

US Patent Sept. 23,1975 Sheet2 0f3 3,907,659

US Patant Sept. 23,1975 Sheet 3 of3 3,907,659

COMPOSITE ELECTRODE AND METHOD OF MAKING SAME BACKGROUND OF THE INVENTION This invention relates to electrodes used in electrolytic cells, e.g., of the type used in copper electrowinning.

Electrodes, such as anodes in copper electrowinning, require high electrical conductivity and good resistance to chemical corrosion. Materials such as platinum, paladium, and gold meet these two requirements, but are prohibitively expensive. Aluminum and copper have good electrical conductivity and are relatively cheap, but are rapidly corroded or dissolved in an electrolytic cell used for copper electrowinning. Titanium has good resistance to corrosion, but it is moderately expensive, and it has poor electrical conductivity. Lead has been the historical compromise because it has fairly good electrical conductivity, and its rate of corrosion is usually acceptable as an economic loss. However, the introduction of lead corrosion products into the electrolyte produces an undesirable contamination of the copper cathode product.

Considerable effort has been spent in attempting to develop electrodes made of titanium, which apparently is the lowest cost metal completely resistant to anode corrosion. One line of work has centered on the use of metal oxides on the titanium surface to reduce the oxygen overvoltage and therefore, power consumption per pound ofproduct. The object of this approach is to reduce power consumption, and eliminate lead contamination, which together might justify the high investment in titanium. To date, the results have not been successful.

The high cost associated with titanium electrodes is largely attributable to the relatively poor electrical conductivity of the metal. For current densities prevalent today, and an allowable maximum of difference in current density between the top and bottom of the anode, an anode thickness of about one-half inch is required, costing more than three times that of a lead anode with the same performance characteristic.

One means of reducing the cost of titanium is to form a sandwich consisting of thin outer layers of titanium, for corrosion resistance, with a central layer of copper or aluminum for good electrical conductivity. Although cladding of nickel, copper and chromium alloys on carbon steel sheets has been practiced to provide corrosion resistance or strength, the process of bonding is typically expensive and difficult, involving problems of achieving and maintaining continuous intimate adhesion over a substantial area, particularly when the electrode is subjected to differential thermal expansion. Similar developed commercial technology for bonding titanium to copper, aluminum or silver is unavailable.

This invention provides a composite sandwich electrode which utilizes the springiness of pieces of metal having a substantially greater electrical conductivity than that of titanium. This springy metal is highly compressed between two relatively thin sheets of titanium,

vwhich are sealed around their edges to provide a protective envelope for the metal of higher conductivity compressed between the two titanium sheets.

cal contact required between the copper plate and the two thin titanium outer sheets.

In terms of method for making the electrode, the invention includes the step of disposing a first thin layer of pieces of metal of good electrical conductivity on a first thin titanium sheet of suitable dimensions and thickness. The pieces of metal of good conductivity all lie within the edges of the titanium sheet. A thin plate or mesh of metal of good electrical conductivity is disposed on the first layer of metal pieces. This plate or mesh also lies inside all edges of the titanium sheet. Alternatively, on one side of the anode, which is the top of the anode, the metal plate or mesh protrudes sufficiently for attachment of the electrode to conducting hanger bars, which are part of the equipment in a standard electrolytic cell. A second layer of metal pieces is disposed on top of the metal plate or mesh. The second layer of metal pieces covers an area coextensive with that of the first. A second sheet of titanium identical with the first is disposed on the second layer of metal pieces. The resulting sandwich is then subjected to high pressure to compress the metal pieces into good contact with each other, with the central plate or mesh, and the interior surfaces of the titanium sheets. While the sandwich electrode is so compressed, the adjacent titanium edges are welded closed to form a hermetically sealed envelope. In the embodiment in which the metal plate or mesh protrudes from the top of the anode, the titanium-metal plate or mesh seams are brazed closed. The electrode is now ready for attachment to electrically conductive hanger bars in a standard electrolytic cell. In the embodiment in which the metal plate in the center of the anode does not project beyond the edges of the anode, a window may be cut in the top portion of one or both titanium sheets to provide direct access to the plate within the anode. The hanger bars are then clamped over the window to make good contact with the plate inside the anode. A gasket may be used between the hanger bars in the area of the titanium sheets around the window to keep the interior of the anode hermetically sealed.

These and other aspects of the invention will be more fully understood from the following detailed description and the accompanying drawings in which:

FIG. 1 is a side elevation of one embodiment of the electrode of this invention ready for attachment to hanger bars in an electrolytic cell;

FIG. 2 is a view taken on line 2-2 of FIG. 1;

FIG. is an enlarged view of a portion of the anode taken in the area 3-3 of FIG. 2',

FIG. 4 is a longitudinal sectional view taken in a plane perpendicular to the major plane of the anode in which the titanium sheets are sealed entirely around their respective peripheries, and respective windows are provided in each of the titanium sheets to permit good electrical contact with the interior of the anode;

FIG. 5 is a view taken on line 5-5 of FIG. 4;

FIG. 6 is a longitudinal sectional view taken from a plane perpendicular to the major plane of an alternate embodiment of the anode; and

FIG. 7 is a view taken on line 7-7 of FIG. 6.

Referring to the drawings, an electrode 10 includes a rectangular thin copper sheet 12 which is sandwiched between first and second layers 16 and 17, respectively, of work-hardened copper wool compressed to a density of about three times that of its normal free density of about 12 lbs. per cubic foot.

The copper plate and the two layers of compressed copper wool are sandwiched between first and second thin rectangular titanium sheets 18 and 19, respectively, which are congruent. The titanium sheets are identical in size and shape, and three edges of the sheets extend slightly beyond three corresponding edges of the copper plate. A fourth edge 14 of the copper plate extends a substantial distance beyond the corresponding edges of the titanium sheets to provide means for attaching the electrode to a hanger bar (not shown) in a conventional electrolytic cell (not shown).

The layers of copper wool overlay the adjacent faces of the copper plate with which they are in contact. The side and bottom edges (as viewed in FIG. 1) of the titanium sheets are welded together. The adjacent portions of the top edges of the titanium sheets are also welded together, and the titanium-copper seams 21 are formed where the copper plate extends beyond the edges of the titanium sheets are closed by brazing so that the titanium sheets form a hermetically sealed envelope around the copper plate and layers of copper wool sandwiched between the two sheets of titanium.

The electrode shown in FIGS. l-3 is fabricated as follows. The first sheet of titanium is laid horizontally on a suitable work surface (not shown). The first layer of work-hardened copper wool is placed on top of the first titanium sheet. The wool all lies within the edges of the first titanium sheet. The copper wool layer is initially about /a inch thick. It subsequently is compressed to about one-third that thickness. Alternatively, metal particles can be used in place of work-hardened copper wool, for example, work-hardened shredded copper can be used, and so can aluminum or silver. However, copper provides the best electrical conductivity per unit cost at the present time, and is the presently preferred material.

The thin copper plate is laid over the first layer of copper wool. The plate lies inside three edges of the titanium sheet. On the fourth side, which is the top of the anode when installed in the electrolytic cell, the copper plate protrudes sufficiently for attachment of the electrically conducting hanger bars used in a conventional electrolytic cell. A copper mesh screen can be used in place of plate material, and the silver and aluminum can be substituted for copper. However, copper is presently preferred for the reasons stated above.

The second layer of work-hardened copper wool is laid on top of the copper plate, and is then covered by the second sheet of titanium. The sandwich is compressed to reduce the volume of the copper wool to about one-third its normal free volume.

With the sandwich held in the compressed state, the three adjacent titanium edges are welded together, and the titanium-copper seams are closed by brazing. The electrode is now ready for attachment to the hanger bars in a conventional electrolytic cell.

The composite electrode of this invention uses the springiness of work-hardened copper wool, shredded copper, or other metal of suitable electrical conductivity and springiness to provide the macroscopically continuous uniform electrical contact required between the copper plate and the titanium sheets.

In operation, the current flows through the hanger bar, the copper core, and through the compressed copper wool to the titanium sheets, essentially evenly throughout. The copper wool is so tightly compressed that it almost becomes a solid piece, yet it still has sufficient resilience to maintain the required electrical contact with its containing walls indefinitely, and accommodate differential thermal expansion and contraction due to the different metals in the electrode being subjected to varying temperatures.

In place of metal wool or shredded metal particles for the springing action, metal pellets or sharp pointed pieces such as tetrapods could be used. Regardless of the exact composition of the resilient layers, they are in any event sufficiently compressed before the electrode parts are bonded together, and after the bonding takes place the resilient layers exert an expansive force which is confined by the titanium sheets being placed in tension.

The interior of the anode can be filled with an inert gas, say nitrogen, to prevent any corrosion of the metal core. However, as far as copper oxidation reducing the eventual effectiveness of the copper wool contacts, filling with an inert gas is not necessarily required. If the electrode is sealed with air contained, the weight of copper wool in a typical electrode is many thousand times greater than that of the trapped oxygen, so that a small fraction of the wool effectively scavenges any oxygen which may be present.

Referring to FIGS. 4 and 5, which show an alternate embodiment of an electrode 29 of this invention, a rectangular copper plate 30 is sandwiched between a first layer 32 and a second layer 33 of copper wool held' in a compressed state by opposing first and second thin, rectangular titanium sheets 34, 36, respectively. Each titanium sheet is a stamping which includes a main flat rectangular portion 37 that holds a respective layer of copper wool. A separate wall 38 perpendicular to the main plane of the depressed section extends entirely around the perimeter of the depressed section of each sheet and projects towards the opposing sheet. A separate flat outwardly extending flange 40 is formed integrally with the edge of each wall remote from portion 37, and mates against a matching flange on the opposing sheet. The upper (as viewed in FIGS. 4 and 5) portion of the flange 40 is substantially wider, than the portion of the flange around the remainder of the portion 37. The two opposing flanges of the titanium sheets are welded together around their entire peripheries to form a hermetically sealed enclosure for the copper wool layers and the copper plate. As shown best in FIG. 5, the edges of the copper plate slightly overlap the inner portions of the flanges 40, except at the top where the upper edge of the copper plate terminates just short of 'the upper edge of the titanium sheets. With this arrangement, when the titanium sheets are pressed together for welding, the edges of the copper plate are squeezed between the inner portions of the flanges so that the copper plate is held firmly in place.

A rectangular window 42 is in each of the upper flanges of the titanium sheets. The windows are collinear and filled with compressed copper wool 44. A separate rectangular gasket 46 fits on the outer face of each flange 40 around a respective window 42. The gaskets, flanges 40, copper wool 44, and copper plate 30 are sandwiched between two elongated parallel copper hanger bars 48, which each cover a respective window and are held in position by a bolt 50 passing through collinear holes 52 in the hanger bars, and through the titanium sheet windows 42, copper wool 44, and a hole 54 in the copper sheet. A nut 56 on the bolt keeps the hanger bars clamped firmly against the outside faces of the titanium sheets, and insures a hermetic seal and a good electrical contact between the hanger bars, the titanium sheets, the copper wool in the windows, and the copper plate. The gaskets keep this electrical contact free from exposure to any ambient corrosive atmosphere which may be associated with the electrolytic cell (not shown) in which the electrode is used.

The advantage of the embodiment shown in FIGS. 4 and 5 is that the electrode does not require brazing titanium-copper seams closed. Instead, the hermetic seal is formed entirely by welding titanium to titanium,

and by sealing around the windows in the titanium sheet with a gasket, which may be of any suitable inert material such as teflon.

Another form of electrode 59 shown in FIGS. 6 and 7 includes a thin rectangular copper plate 60 sandwiched between a first layer 61 and a second layer 62 of copper wool, which are held tightly compressed against the opposite faces of the copper plate by first and second thin rectangular titanium sheets 64 and 66, respectively. The titanium sheets are welded together at their edges around their entire peripheries to form a hermetically sealed enclosure for the copper plate and copper wool.

A pair of elongated parallel copper hanger bars 68 are clamped firmly against the outer faces of the upper edges of the titanium sheets by nuts 70 and bolts 72 extending through the copper hanger bars on opposite sides of the electrode 59.

The electrode shown in FIGS. 6 and 7 has the same advantage as the one shown in FIGS. 4 and 5, namely, the titanium sheets are welded together to form a hermetic seal without requiring titanium to copper brazing. The embodiment shown in FIGS. 6 and 7 also eliminates the need for a window in the titanium sheets, and a gasket required to seal around those windows. The electrical resistance offered by the anode shown in FIGS. 6 and 7 will be somewhat greater than those shown in FIGS. 1-5 because the current from the copper hanger bars must pass through the thin titanium sheets before reaching the copper wool and copper plates within the electrode. Nevertheless, the arrangement shown in FIGS. 6 and 7 provides a chemically inert anode which has a much greater electrical conpieces of metal are selected from the group consisting of work-hardened copper wool and shredded copper.

3. An electrode according to claim 1 which includes a copper core embedded in the mass of the pieces of metal.

4. An electrode according to claim 1 which includes a copper plate embedded in the mass in the pieces of metal and projecting outwardly from the envelope to provide means for attaching the electrode to a hanger bar.

5. An electrode according to claim 1 in which the mass of pieces of metal is compressed to a volume substantially less than its normal free density.

6. A composite electrode comprising a pair of opposing sheets of titanium spaced apart in a central portion and sealed together entirely around their respective peripheries to form a hermetically sealed envelope between the two sheets, a plate of metal having an electrical conductivity substantially greater than that of titanium disposed within the envelope and spaced from the titanium sheets, and pieces of metal of greater electrical conductivity than titanium packed in the space be tween the plate and the titanium sheets. 

1. A COMPOSITE ELECTRODE COMPRISING A PAIR OF OPPOSING SHEETS OF TITANIUM SPACED APART IN A CENTRAL PORTION AND SEALED AROUND THEIR EDGES TO FORM AN ENVELOPE, AND A MASS OF PIECES OF A METAL HAVING A SUBSTANTIALLY GREATER ELECTRICAL CONDUCTIVITY THAN THAT OF TITANIUM DISPOSED IN A COMPRESSED STATE WITHIN THE ENVELOPE.
 2. An electrode according to claim 1 in which the pieces of metal are selected from the group consisting of work-hardened copper wool and shredded copper.
 3. An electrode according to claim 1 which includes a copper core embedded in the mass of the pieces of metal.
 4. An electrode according to claim 1 which includes a copper plate embedded in the mass in the pieces of metal and projecting outwardly from the envelope to provide means for attaching the electrode to a hanger bar.
 5. An electrode according to claim 1 in which the mass of pieces of metal is compressed to a volume substantially less than its normal free density.
 6. A composite electrode comprising a pair of opposing sheets of titanium spaced apart in a central portion and sealed together entirely around their respective peripheries to form a hermetically sealed envelope between the two sheets, a plate of metal having an electrical conductivity substantially greater than that of titanium disposed within the envelope and spaced from the titanium sheets, and pieces of metal of greater electrical conductivity than titanium packed in the space between the plate and the titanium sheets. 